Beam Energy Measurements for Mott Run II : Dry run for Bubble Beam Energy Measurements for Mott Run II : Dry run for Bubble ? Joe Grames March 9, 2016

Oct 2015 studied Mott analyzing power vs. beam energy. Varied beam kinetic energy 4.5-5.3 MeV in 0.2 MeV steps. Record cavity gradient, Bubble dipole, steering coils, beam positions. q = 25.0°

TN provides model for ideal operation with dP/P = 0.1% J. Benesh, “A detailed examination of the MDL field map and the TOSCA model of this “5 MeV” dipole”, JLab-TN-15-017. TN provides model for ideal operation with dP/P = 0.1% BL = M0 + M1 P + M2 P2 + M3 P3 + M4 P4 + M5 P5 M0 = +4.811 M1 = -1416.2 M2 = +1.2399 M3 = -0.1646 M4 = +0.009795 M5 = -0.00021257 R028 MDL0L02 P dP MV/m G-cm MeV/c 3.35 7109.57 5.035 0.005 3.74 7384.34 5.229 4.12 7646.01 5.415 4.5 7927.59 5.614 0.006 4.89 8185 5.797

Magnetic fields other than dipole play important role: Stray By field (red points) from Earth and Ion Pumps Distributed mu-metal helps shield beam from stray field Steering coils provide distributed point-correction Constructed simple model to track fields Plots show trajectories for 4.5-6.5 MeV/c in 0.5 MeV/c increments Without steering coils beam is “lost” to pipe wall x=1.75cm With steering coils orbit is realistic and quasi-independent of momentum With Stray. Without Mu-Metal, Steering Coils With Stray, Mu-Metal, Steering Coils

Record SRF gradient, steering coils, Bubble dipole and beam positions. Convert recorded beam positions (.XPOS) to absolute survey positions (.XCOR). Assumed calibration of beam position monitor to quadrupole s = 0.50 mm Assumed survey of quadrupole to absolute coordinates s=0.25 mm

Model trajectories using beam positions and propagate uncertainties Use 0L BPM’s to constrain orbit and predict beam (X,X’) at dipole MDL0L02 Use (X,X’) at dipole and 5D BPM’s to determine how much q <> 25.0° Correct Jay’s model calculation proportionally : PTOSCA(25.0°)[25.0°/(25.0°+q)] Model of Undeflected 0L beam line Model of Deflected 5D beam line Model predicts dipole deflected beam in excess of 25.0° by <q>: <q> = 1.311 ± 0.267 mrad = 0.0751° ± 0.015°

Error budget for Mott Run II Summary for Mott Run II Recommendations for Bubble Shielding helpful, but probably not global solution => still need model Improve beam position monitoring around (0L) or further from (5D) dipole Greatest “bang for effort” systematic study of model for non-ideal orbits